He remained in the Regular Army after the close of the Civil War and was promoted to captain, March 14, 1866. He was commanding a company, dept. quartermaster, and chief quartermaster District of Minnesota; Fort Snelling, Minn., from May, 1866, to May, 1867; on leave of absence from May to October, 1867 ; commanding company at Fort Snelling, Minn., to April, 1869; unassigned May, 1869 ; on duty at Galveston, Indianola, Corpus Christi, and Jefferson, Texas, 1869.[1]

During the Red River War, 1874-76 he again was commanding Company G, at Fort Griffin. On February 5, 1874, detachments of Companies A and G, Eleventh Infantry, attacked a camp of hostile Qua ha dee Comanches on the Double Mountain Fork Brazos River, Texas, killed eleven Indians and captured sixty-five horses. One enlisted man was wounded in the fight.

On May 16, 1877, Lt. Gen. Sheridan directed his brother Lt. Col. Michael V. Sheridan to retrieve the bodies of Custer and his officers. On June 20, 1877, About 7 o'clock Company I, Seventh Cavalry (Captain Nowlan), reached the north bank of the Yellowstone, having been detached as the escort of Colonel Sheridan, who was to proceed to the Little Bighorn for the purpose of securing the bodies of the officers who fell in the Custer fight. Later in the day Colonel Sheridan passed up the river on the steamer Fletcher, being accompanied by Captain Schwan, Company G, Eleventh Infantry.

Headquarters of the Military District of Dakota Territory, March 15, 1878, designated Capt. Theodore Schwan to act as Indian agent at the Cheyenne Agency, Dakota Territory. [3] On June 20, the commissioner of Indian Affaires instructed Captain Schwan to form an Indian police force on the Cheyenne River Agency in order to reduce the need of a military force at the agency.[4]

Two weeks before his last promotion in the regular army he was appointed brigadier-general of volunteers, and in accordance with the Act of Congress, approved March 2, 1899, he will retain that rank until July 1, 1901. He was brevetted several times.[7]

When the Spanish-American War erupted, Lt. Col. Schwan was appointed brigadier general of volunteers and colonel in the Regular Army in May 1898, making him one of the only foreign-born generals in the Spanish-American War. He assumed command of the First Division of the Fourth Army Corps, which had mustered in at Mobile, Alabama before moving to the Tampa assembly area in early June and Miami, Florida on June 20.[8] That unit was exchanged with the First Division, Seventh Army Corps on June 27, and at the beginning of July, Schwan was relieved of that command by the War Department, freeing him for service with the Puerto Rican invasion.[9]

Schwan assumed command of the Independent Regular Brigade and sailed for Puerto Rico; the brigade landed at Guánica on July 31 and moved west along the coast.[10] On August 10, his brigade won the Battle of Silva Heights; the next day, he entered the town of Mayagüez, Puerto Rico.[10] The Spanish moved up for another attack on Schwan, but a cease fire was enacted before either side attacked. Allegedly during this cease fire, Schwan's troops engaged in the first game of baseball to be played in Puerto Rico.

With the fighting on Puerto Rico over, General Schwan was transferred to the Philippines, where he became chief-of-staff of the Eighth Army Corps, which had become engaged in the Philippine-American War. He personally directed the first Cavite Expedition, then took command of the Second Brigade in the corps' First Division (in this era, brigade and division numbers were repeated from one corps to another) during the second Cavite Expedition.

First Lieutenant, 10th U.S. Infantry. Place and date: At Peebles Farm, Va., October 1, 1864. Entered service at: New York. Born: July 9, 1841, Germany. Date of issue: December 12, 1898.

Citation:

At the imminent risk of his own life, while his regiment was falling back before a superior force of the enemy, he dragged a wounded and helpless officer to the rear, thus saving him from death or capture.[12][13]

^Report and historical collections, Volume 28, South Dakota. Dept. Of History, South Dakota State Historical Society, State Pub. Co., 1956.

^General orders, United States. War Dept, United States Adjutant-General's Office, United States Military Secretary's Dept Publisher The Dept., 1887

^Annual report of the Secretary of War, Volume 1, United States. War Dept., 1895.

^Herrmann, Karl Stephen, From Yauco to Las Marias: being a story of the recent campaign in western Puerto Rico by the independent regular brigade, under command of Brigadier-General Schwan, R. G. Badger & Co., 1900.